Problem: The probability that Kim has a math test today is $\frac{4}{7}$. What is the probability that Kim does not have a math test today? Express your answer as a common fraction.
Solution: The probability that Kim does not have a math test is equal to one minus the probability she does have a math test. So, the probability of not having a math test is $1 - \frac{4}{7} = \boxed{\frac{3}{7}}$.